I. Field of the Invention
This invention relates to the controlled oxidation of ethane to produce primarily ethanol with some methanol and little or no aldehyde or acid.
II. Description of Prior Art
This invention relates to the direct conversion of ethane to ethanol (Direct Ethane Oxidation, DEO). Ethanol (C.sub.2 H.sub.5 OH) is presently produced either by the fermentation of sugar (Reaction 1) or by the hydration of ethylene (Reaction 2) which is normally formed by the dehydrogenation of ethane (Reaction 2a). ##STR1## The ethanol cost from these two processes are estimated to be $1.67 and $1.38 US/gal respectively.
Other processes have been described which include the hydrogenation of acetic acid (by Humphreys and Glasgow) and the hydrogenolysis of methyl acetate (by Halcon SD). Ethanol from these two processes is estimated to cost $1.06 and $1.15 US/gal respectively.
Ethane is a by-product recovered from natural gas in the liquified petroleum gas fraction along with propane and butane. Ethane is primarily used to make ethylene (via Reaction 2a) which is used to produce the plastic-polyethylene (polythene). There is presently a surplus of ethane on the world market and it is used as a fuel for its heat value. The estimated cost of ethanol via the DEO process of this invention is approximately $0.53 US/gal which makes it an attractive octane enhancer for gasoline.
Previous attempts to convert ethane directly into ethanol by partial oxidation met with limited success (Newitt and Block, Proceedings of Royal Society, Vol. 140A, p. 426, 1933; Newitt and Szego, Proceedings of Royal Society Vol. 147A, p. 555, 1934; Bell et al, Industrial and Engineering Chemistry Vol. 41, pg. 2609-12, 1949; Shlau and Albright, Industrial and Engineering Chemistry--Process Development Vol. 21, p. 101, 1982).
Only the early workers, Newitt and coworkers, obtained ethanol in significant yields (20 to 60%).
One of the neglected aspects of the oxidation process is the induction period which Bone and Hill (Proceedings of the Royal Society Vol 129A, p. 434, 1930) showed in a static system to decrease with increase in temperature and increase in pressure. In plug flow reactor system this induction period must be dealt with by the use of a pre-heater.
Accordingly, the object of the invention is to provide a process for the direct conversion of ethane to ethanol which is relatively easy to operate and which gives a good yield of alcohol with high selectivity.